The phenotypic characterization of normal and neoplastic cells and their isolation for functional and molecular analysis by flow cytometry is fundamental to cancer research. The Flow Cytometry Shared Resource assists HICCC members in flow cytometry-based studies. The capacity of the facility has increased substantially over the past five years due to the acquisition of new instruments and the hiring of additional personnel. The facility now operates six instruments, including three fluorescence-activated cell sorters and two advanced cell analyzers. The cell sorters allow high-speed cell sorting and can detect up to 12 fiuorescent parameters. One sorter in addition is equipped with a laser that enables detection of the living color fluorescent proteins dsRed and the dsRed derivatives mCherry and tdTomato; one instrument Is placed in a biosafety hood to enable sorting of primary human material. The two advanced cell analyzers besides multi-color fluorescence are able to perform various specialty applications such as multiple fluorescent protein analysis including dsRed derivatives, calcium flux measurements, determination of DNA content in live cells, and identification of the side population. In addition to those sophisticated instruments, the facility provides access to a user-operated basic cytometer permitting four-color immunophenotyping as well as cell cycle and apoptosis assays. The three analyzers are accessible for investigators around-the-clock. The facility manager since 2004 is Ms. Kristie Gordon, who has more than 25-years of experience in operating flow cytometers. The facility director since 2007 is Dr. Ulf Klein, whose past and present research on B-cell malignancies involves the use of various flow cytometrical approaches. Over the last several years, the services of the facility have benefited more than 100 Columbia University Pis, with HICCC members comprising the main clients, accounting for more than 60% of usage. This high usage allows the facility to offer the services at low fees, which are further reduced for HICCC members. The sophisticated equipment available in the facility allows investigators at Columbia to perform the highest state-of-the-art research in the area of fiow cytometry, and therefore represent a vital resource for HICCC members.